Geothermal Heat Pumps

A Geothermal Heat Pump system is a heating and/or cooling system, which uses the earth as a heating resource in the winter or as a heat sink to put the heat back into the ground in the summer. This is made possible because ground temperatures of a certain depth are stable all year long (around 50-60F).

The idea of using the natural heat of the earth to heat houses without consuming extra energy can be dated back to the time of the Roman Empire, when people started to utilize sources of hot water and steam that exist near the surface of the earth to heat buildings. With the development of technology and the reduction of electricity prices, peole are allowed to use geothermal resources anywhere in the world.

Technology basics

A geothermal heat pump system is also known as "GeoExchange"system and "ground-source heat pump". The system ususally requires a length of buried tubing on the property, a liquid pump back and a water-source heat pump. Common systems include open loop systems and closed loop systems.

Open loop systems:

A demonstration of a open-loop system

Source: EERE. Author: EERE. Permission: Public Resource.

Closed loop systems:

A demostration of horizontal closed-loop system

Source: EERE. Author: EERE. Permission: Public Resource.

Closed loop systems are more commonly used in household use. Horizontal systems are more cost-effecitve for residential installations. While, vertical systems are usually used for commercial buildings and schools. The closed loop system circulates the fluid through the loop pipes and exchange heat between the fluid and the earth across the pipe.

Advantages and Disadvanges

Geothermal heat pump systems have many advantages compared to conventional systems in ternms of energy saving, duration and envrionmental influencs. However, heat pumps do have disadvantages such as a higher cost for initial installation.

Advantages

Compared to conventional systems, geothermal heat pump systems have notable advantages in saving energy, duration, saftey and environmental influence.

Reduced Electricity Costs - Geothermal heat pump systems save from 30% to 70% energy over conventional systems,¹ since they simply use electricity to move heat from the earth into buildings instead of burning fuels to generate heat. Geothermal heat pumps systems thus bring in higher efficiencies up to over 400% compared to conventional systems. ²Study shows these systems can save the average family from US $400 to $1400 per year.³ In the summer, the domestic hot water is produced for free and at a small cost in the winter.
Durability and Reliability - Geothermal heart pumps systems have a longer life span than conventional systems. Most loop fields are warranted for 25 to 50 years and are expected to last at least 50 to 200 years. ⁴You do not have to worry about replacing the system in the short term and once installed, systems can last twice as long as conventional systems.
Convenience and Safety - Close loop systems mean no freezing of the flue vents in the cold weather when you need heat the most. Also, there are no gas lines that have potential for a gas leakage or fire.
Environmental Benefits - The switch from fuel to electricity reduces greenhouse gas emissions. There are more than 1,000.000 geothermal heat pumps already installed in the U.S.⁵ and the technology has reduced an estimated more than 5.9 million metric tons of CO2 annually and more than 1.6 million metric tons of carbon equivalent annually.

Disadvantages

One disadvantage is that the initial installation cost of GHPs is more expensive than a comparable gas-fired furnace and central air-conditioning system. (More discussions about cost can be found below.)
Open-loop systems have more potential problems than either conventional systems or closed-loop geothermal systems because they bring outside water into the unit. This can lead to clogging, mineral deposits, and corrosion in the system. Open loop systems also require a large supply of clean water in order to be cost effective. This often limits their use to coastal areas, and areas adjacent to lakes, rivers, streams, etc.⁶
Refrigerant Loop systems have several disadvantages, including: environmental issues related to the system's use of refrigerant, corrosion issues since they use copper piping which needs anodic protection, and the need to maintain refrigerant temperatures within certain limits to keep from freezing or baking the ground, difficulty in finding and fixing a refrigerant loop leak, should one occur. ⁷

The Cost for Household

The initial cost of installing a geothermal heat pump system is usually two or three times than of a conventional heating system. ⁷However, some electricity companies offer special rates to customers who install geothermal systems, simply because it helps reduce their peak load.

Geothermal heat pumps save money in operating and maintenance costs. Properly sized and installed GHPs deliver more energy per unit than conventional systems.

Research and Development

The Department of Energy's (DOE) Geothermal Energy Program focuses on energy system research and testing, drilling technologies and geoscience and supporting technologies.